Free and Open Source software (FOSS) is one of computer software, which source code can be accessed, freely used, modify, and distribute by anyone. It is produced by many of people or organizations, and distributed under licenses that comply with the open source definition. This software has recently begun to play an important role in the academic and scientific research field, as in the professional field. In the past few decades, Geographic Information Systems (GIS) has seen very high growth rate, and this development included each of commercial and open source GIS software. This research aims to show the great potential of Free and Open Source Geographic Information Systems (FOSS_GIS), and motivating to adopt it in developing countries, as a means to reduce licensing costs, promote local technological development through access to the source code and developing these systems. A case study is taken, in which we have tried to highlight the most important advantages of this software (i.e. FOSS_GIS), such as ease of implementation and good use, the ability to analyze and display of spatial data, professional maps production, and functionality emulator to commercial GIS software. The case study included the methodology of spatial suitability analysis, which is one of the main tasks of GIS; this methodology has been applied to choose the optimal site of urban project in Sheikh Badr area (Tartous Governorate) by proposing a set of general conditions. Using optimal site selection analysis of urban project helps to avoid the indiscriminate expansion and the irregular land-use. The free and open source software QGIS was used in this research, as well as the algorithms and tools of GRASS and SAGA softwares. Key Words: FOSS_GIS, spatial analysis, QGIS, optimal site selection, Sheikh Bader area